The goal of this project is to analyze bronchioalveolar carcinoma (BAC) tissues for type II pneumocytic differentiation. Identification will be made of a subgroup of BAC of the lung derived from type II pneumocytes. These tumors will be identified by using antisurfactant apoprotein antibody and immunohistochemistry techniques. The tissues will be gathered retrospectively from several collaborating institutions. Identification of patients with this rare tumor will: (1)\define the light microscopic criteria for diagnosis of type II pneumocyte-derived carcinomas; (2)\provide clues to the etiology of this rare neoplasm; and (3)\establish the clinical features and behavior of these tumors. Epidemiological information including age, sex, smoking history, occupation, and co-existing pulmonary diseases will be collected. The natural history of the tumor will be studied and the response to therapy evaluated. (4)